1. Field of the Invention
The present invention relates to a temperature controlled cooling system and, more particularly, to a microprocessor controlled fluid circulating system for medical uses.
2. History of the Prior Art
Recent clinical evidence indicates that if the temperature of a body part, particularly a wound site, is lowered a number of therapeutic benefits ensue. First, a lower temperature will reduce swelling and increase the activity of the blood in the wound area to promote healing. Second, a lower temperature at a wound site substantially reduces the pain experienced by the patient. This not only increases the comfort level of the patient but significantly reduces the necessity for the administration of narcotics and other pain medication to the patient's benefit. Third, reduction of the temperature at a wound site increases the flexibility in that region. This is particularly true in the case of a traumatized joint or at the installation site of an artificial joint, where a lower temperature will greatly increase the ability of the patient to exercise the joint. Such treatment can substantially reduce the required period of stay in the hospital.
Initial use of cooling therapy was mainly found in the field of orthopedics. It is now found that post surgical cooling is highly beneficial in the reduction of trauma to the patient. It also increases the rate of healing and reduces the length of a hospital stay. In addition, cooling therapy is also being used in home health care for chronic pain control and to increase joint flexibility and facilitate the rate of healing.
Numerous prior art devices have been proposed for reducing the temperature of a body part in order to achieve the beneficial results obtained thereby. For example, ice packs have long been used to reduce swelling and achieve some of these benefits. In addition, cold packs containing two chemicals, which when mixed together absorb heat (endothermic reactions), have also been proposed as have cooling pads through which a cooling fluid is circulated and cooled by means of a compressor and refrigerant condensing in evaporator coils. Such devices are very inconvenient and contain many inherent disadvantages.
More recently, devices for circulating a cooling fluid through a blanket applied to a patient have also been proposed. Examples of such structures are shown in Kumar U.S. Pat. No. 3,894,213, and Brown U.S. Pat. No. 3,967,027, and Bailey U.S. Pat. No. 4,459,468. The Bailey patent discloses an apparatus which employs a fluid reservoir for containing a substantial volume of cooling fluid, the temperature of which is regulated by thermal modules. The temperature of the fluid in the reservoir is monitored to maintain a selected temperature. The fluid is pumped from the reservoir through a hose system to a thermal blanket which is applied to the patient and back into the reservoir for further cooling. While such a system has been popular in medical applications, it includes numerous disadvantages. For example, a reservoir system, such as that found in Bailey, requires a substantial pre-cooling time in order to reduce the temperature of the relatively large mass of fluid in the reservoir to a desired temperature level. Secondly, such fluid reservoir type systems must also be primed or go through a priming cycle before use to ensure that there is sufficient fluid in the reservoir before performing the cooling operation. Thirdly, the temperature of the reservoir fluid must be monitored and used as the control parameter. This leads to extreme inaccuracy in attempts to maintain a precise control over the temperature applied directly at the wound site. The heat gained by the fluid between a fluid reservoir and a thermal blanket may often be reflected by a temperature increase as much as 10 to 15 degrees. This results in a very inaccurate regulation of the actual temperature at the wound site.
Another problem associated with the applications of very cold surfaces, such as that of an ice pack, directly to a body part is its effect on the skin. The temperature of the ice pack is very cold and can only be left against the skin for a short period of time. Generally, leaving it longer than 30 minutes can result in damage to the skin. It is much more desirable to be able to apply a temperature in a range between 50 and 55 degrees, which is relatively comfortable to the skin, and maintain that temperature for a substantial number of days. This prolonged application insures that the body part is cooled to the inner depth of the bone or tissue of the traumatized area. With an ice pack, cooling only takes place in the subdural area. In a more precisely controlled temperature application, cooling can take place at a deep penetration for an extended period. Thus, it is highly desirable to be able to maintain precise control of the temperature which is actually contacting the tissue of a wound site and then sustain that temperature for a substantial period of time. In this manner the advantages obtained from the use of cold therapy in a medical application can be vastly increased.
It would thus be highly desirable to be able to provide a fully programmable temperature controller for medical applications in which the temperature actually applied to the wound site could be very carefully monitored and controlled. In addition, it would be desirable to be able to produce more immediate cooling and a digital read out of that cooling to a monitoring computer. The variations of the actual temperature of the wound site over a substantial period of time could be used in medical studies and other applications. Such a system could also be programmed to monitor any anomalous conditions in the system such as insufficient amounts of circulation fluid or losses of pressure due to leakage or defective couplings.